The crew of the flight from Urumqi, in the west, to the central city of Wuhan, discovered the passenger's actions after take-off, the official Xinhua news agency reported.

Police said a man and a woman were arrested after the flight landed, according to Xinhua.

The case is under investigation, the report said, giving no further details.

The security situation is more tense in Xinjiang than other parts of China because Beijing says it faces a serious separatist threat in the region.

Exiled members of the region's Muslim Uighur majority say Beijing exaggerates the threat to justify harsh controls in the region, which is rich in energy reserves and borders several central Asian countries, AFP informs.

In March 2008, authorities said they foiled an apparent terrorist attack on a flight from Xinjiang to Beijing. In that incident, two people including an ethnic Uighur woman had been arrested after a passenger was caught trying to ignite fuel inside the plane's toilet.

Tensions continue to simmer in Xinjiang between majority Muslim Uighurs and Han Chinese.

Ethnic riots in Urumqi in July last had left 197 people dead and thousands injured. Chinese authorities last month had executed nine Uighurs over the riots.

Xinjiang's 21 million population is divided mainly between Uighurs, a Turkic-speaking Muslims and Han Chinese, RTT News reports.